The present invention relates to a Hadamard transformer using charge transfer devices.
U.S. Pat. No. 4,357,677 describes a device which comprises:
a charge transfer device comprising a plurality of electrodes arranged in a line,
an input circuit able to form, on the basis of an input signal, sequences of N samples, which are the samples to be transformed, followed by the conversion of each sample into charge packets or groups, injecting the latter at appropriate times beneath appropriate electrodes of the charge transfer device,
a control circuit for the transfer of charges from one electrode to the next,
a differential charge reader constituted by two charge measuring circuits and a differential amplifier with two inputs, one being a reversing input and the other a non-reversing input and each connected to one of the measuring circuits, certain of the electrodes, called reading electrodes, being connected to one or other of the two measuring circuits, so that each electrode makes a positive or negative contribution to the formation of the reading signal,
a circuit for the formation of output samples from the signal supplied by the differential reader.
The arrangement of the electrodes and the control of the times for the injection and the transfer of charges beneath these electrodes are such that at each output sample formation time, the N groups of charges corresponding to the N input signals are located beneath reading electrodes, whose signs relative to the respective contributions correspond to the signs of the linear relation coefficients linking the output sample with the N input samples.
A disadvantage of certain of the devices described in the aforementioned patent is that for transformations with a rank higher than 2, the charge transfer frequency must be a multiple of the sampling frequency. This is more particularly the case for the variant in which the charge transfer device comprises N.sup.2 reading electrodes (N&gt;2) distributed into N groups of N electrodes each, the sequence of the signs of the electrodes of one group being identical, with the sequence reversed, of the signs of a row of the matrix representing the transformation. In this case, the input circuit injects the charge groups beneath the first electrode of the first group and the transfer frequency is equal to N times the sampling frequency.
Moreover, with the devices of the aforementioned patent, it is necessary to use two charge transfer rows operating in alternating manner, one carrying out the actual transformation operations, while the other receives the new samples to be processed and vice versa.